The invention relates generally to computer systems and deals more particularly with an efficient technique for transferring messages and data between virtual machines, logical partitions or application programs.
There are many computer environments in which two or more computer entities need to exchange messages or data. Such computer entities include virtual machines, logical partitions and applications running on a unitary operating system such as Unix or Windows NT.
A virtual machine operating system is well known today and comprises a common base portion and separate user portions. In an IBM z/VM operating system, the common base portion is called the “Control Program” or “CP” and each user portion is called a “virtual machine” or “guest”. Many applications can run on each virtual machine. Each virtual machine has its own work dispatcher (and associated work queue) and appears to the user and his or her applications as a personal operating system. Each virtual machine executes commands on behalf of the applications they support. The different virtual machines can communicate with each other through the common base portion. The communications between the different virtual machines via CP may be in the form of messages conveyed by virtualized communication devices such as Guest Lan or IBM proprietary protocols such as IUCV. Though these communications are conveyed by a variety of protocols, all of these communication mechanisms have at least four common properties:                a) Message data is first written into the sender's virtual address space.        b) An interrupt is generated for each message in each of the receivers' virtual machines.        This invokes interrupt handling in each receiver virtual machine.        c) CP must be invoked in order to accomplish the communication.        d) CP copies message data from the sender's virtual address space to all of the receivers' virtual address spaces.With the foregoing communication methods there is significant overhead associated with invoking CP, generating interrupts, processing interrupts, and copying the message data from the sender's virtual address space to the virtual address space of each of the receivers.        
The following is a more detailed description of IUCV. IUCV is an IBM proprietary point-to-point protocol. A point-to-point protocol transfers data from one sender to one receiver. To communicate via IUCV, a sender first invokes CP indicating the identity of the intended receiver of communication. CP generates an interrupt to the receiver and if the receiver agrees to communicate, CP provides the receiver with a communication path id. CP also then interrupts the sender and provides the sender with the communication path id. To send data, the sender invokes CP indicating the previously obtained path id and the data to be sent. CP uses the path id to identify the receiver and generates an interrupt to the receiver. The receiver responds to the interrupt by invoking CP to receive the data. CP then copies the data from the sender's virtual address space to the receiver's virtual address space and generates an interrupt to the sender indicating that the data has been transferred.
The following is a more detailed description of Guest Lan. Guest Lan is a virtualized communication device using local area network (LAN) protocol. Lan protocol allows communication between a sender and multiple receivers simultaneously. To communicate via a Guest Lan, both sender and receivers invoke CP indicating that they wish to participate in the Guest Lan. To send data, the sender invokes CP indicating the data to be sent and which receivers should get the data. CP generates an interrupt for each identified receiver. The receivers each respond by invoking CP to receive the data. CP then copies the data from the sender's virtual address space to the virtual address spaces of each of the receivers. Once all receivers have received the data, CP generates an interrupt to the sender indicating that the data has been transferred to all receivers.
A logical partition environment is also well known today. A logical partition is a logical division of resources of a single computer system, which division is accomplished by software and microcode. Each logical partition is defined by a respective configuration of CPU(s), memory and peripheral devices. An operating system running in a logical partition views its logical partition as nearly indistinguishable from a real computer, although the logical partition may provide some additional services not available on a real machine. Therefore, the operating system is largely unaware that it is running in a logical partition, and is largely unaware of other logical partitions of the same real computer. Each logical partition also has its own dispatcher, and uses interrupts to communicate messages/data from one logical partition to another as in the virtual machine environment.
There are other known techniques for one application to communicate with another application when both applications are running on the same operating system, such as Windows NT or Unix. In this environment, the operating system utilizes the same dispatcher for both applications. According to these known communication techniques, when application “A” wants to communicate with application “B”, application A calls/notifies the supervisor within the operating system. The call includes the address of the message/data in memory accessible by application A. In response, the supervisor copies the message/data to a location that application B can access. Next, the supervisor puts a work element on the dispatch queue. The work element identifies application B as the recipient, and includes a command to fetch the message/data. Then, the dispatcher dispatches the work element to application B at a time consistent with the dispatching strategy of the operating system and the relative priorities of the work elements. The following are some of the possible, known dispatching strategies. If application B is not currently busy, then the message/data work element is dispatched to application B when the processor becomes free and/or is not occupied with processing higher priority work elements (for any application). If application B is currently busy with another, lower priority work item, then the dispatcher may substitute the message/data work item when the lower priority work item completes its allotted processor time slice or makes a call to the operating system. But, it would not be appropriate to “interrupt” the operating system to convey the message/data to application B because of the overhead involved. The sharing of the dispatcher makes this unnecessary. As noted above, virtual machine, logical partition and other environments do not have a common dispatcher.
An object of the present invention is to provide an efficient method for communication/data transfer between (a) two different virtual machines running on the same base operating system, (b) two logical partitions of the same computer or (c) two applications running on the same computer but having different dispatchers.
An object of the present invention is to provide an efficient method for communication/data transfer from (a) one virtual machine to two or more other virtual machines all running on the same base operating system, (b) from one logical partition to two or more other logical partitions of the same computer or (c) one application to two or more other applications running on the same computer but having different dispatchers.